1. Field of the Invention
The present invention relates to a route searching device of a vehicle, more particularly to a route searching device that searches a running route whose fuel consumption amount is minimized when the vehicle runs from a departure point to a destination.
2. Description of the Related Art
For example, Japanese Patent Application Laid-Open No. 2-278116 discloses a navigation system. In the navigation system, a necessary time in each interval, a running distance, fuel consumption between intersections of the route to the destination are stored as a database in each run, and a maximum fuel consumption route is displayed from these pieces of data.
Japanese Patent Application Laid-Open No. 2005-98749 discloses a vehicle navigation system. In the vehicle navigation system, an energy consumption rate is estimated from four pieces of information. The four pieces of information include (a) static information (such as a running distance of each interval and road gradient) on the route, (b) dynamic information (such as a traffic status and a traffic signal status) on the route, (c) vehicle specifications (such as a type of a drive source and performance of the drive source), and (d) a driving characteristic of a driver.
Japanese Patent Application Laid-Open No. 2009-79995 discloses a route searching device. In the route searching device, a carbon dioxide emission amount (fuel consumption amount) of each link from the departure point to the destination is computed as the sum of a fuel consumption amount consumed in an idling state, a fuel consumption amount consumed during constant speed running, and a fuel consumption amount consumed by acceleration from a stopped state to a running state.
Japanese Patent Application Laid-Open No. 10-197272 discloses a vehicle navigation device. In the vehicle navigation device, a fuel consumption coefficient is set according to an urban road, a suburban road, or an expressway, and the fuel consumption coefficient is corrected according to a flat road, a rising gradient, or a falling gradient. An amount of fuel necessary to reach the destination is computed by the fuel consumption rate, the fuel consumption coefficient of each interval, and the running distance of each interval.
In the navigation system disclosed in Japanese Patent Application Laid-Open No. 2-278116, only the maximum fuel consumption route for the interval stored in the database can be searched, but the route cannot be searched when the vehicle runs in the interval that is not stored in the database.
In the vehicle navigation system disclosed in Japanese Patent Application Laid-Open No. 2005-98749, although the energy consumption rate is estimated from the four pieces of information, how to utilize the pieces of information to estimate the energy consumption rate is not specifically disclosed.
In the route searching device disclosed in Japanese Patent Application Laid-Open No. 2009-79995, although traffic jam information and road category are considered in computing the fuel consumption amount, how the road category reflects the computation is not specifically disclosed.
In the vehicle navigation device disclosed in Japanese Patent Application Laid-Open No. 10-197272, the set fuel consumption coefficient for the expressway is smaller than that for the urban road, and the fuel consumption coefficient is uniformly set to each interval. Therefore, the fuel consumption coefficient is not set according to the actual running state.
An object of the invention is to improve the problems of the inventions disclosed in Japanese Patent Application Laid-Open Nos. 2-278116, 2005-98749, 2009-79995, and 10-197272 to search a running route whose fuel consumption amount is minimized by accurately estimating the fuel consumption amount according to the actual running state when the vehicle runs from the departure point to the destination.